472 Bulletin American Museum of Natural History. [Vol. XIX, 



for modifications of the shaft, is much Hke that of Eqnus. 

 The shaft of the radius, in its median portion, is concave 

 behind, forming a sharp angle with the posterior border of 

 the inner face. 



The shaft of the ulna is continuous, but very much reduced, 

 and firmly coalesced with the radius. 



The carpus as a whole is more rounded in contour, and the 

 transverse diameter is proportionately less than in Eqnns. 

 The articulation of the scaphoid and magnum is peculiar. 

 On the distal face of the scaphoid the facets for the articula- 

 tion of the trapezoid and magnum are in form and position 

 practically the same as in Equus, except that the magnum 

 facet extends further backward and curving downward ends in 

 a conical tooth-like process, which in the flexed position of 

 the carpus fits into a corresponding depression in the mag- 

 num. In Equus the scaphoid and magnum do not touch each 

 other when the foot is fully flexed. 



The convex portions of the radial facets of the scaphoid and 

 lunar occupy a relatively larger part of their proximal sur- 

 faces than in Equus. The cuneiform is proportionately small- 

 er than in either Mesohippus or Equus. The pisiform is 

 short, thin, and broad, resemljling that of Equus in propor- 

 tions. The trapezium is very small and rudimentary, and 

 articulates principally with the trapezoid, though there are 

 two other small facets which indicate that the trapezium 

 articulates slightly with the scaphoid proximally and with the 

 rudimentary metacarpal I distally. The unciform is relatively 

 high and narrow, and projects below the distal face of the 

 magnum. 



The metacarpus consists of one principal and two much 

 reduced lateral members, metacarpals III, II, and IV, and 

 two rudimentary bones representing metacarpals I and V. 

 These rudimentary metacarpals are about equal in size and 

 are reduced to mere nodules of bone, which articulate prin- 

 cipally with the second and fourth metacarpals respectively. 

 Metacarpals II and IV are nearly as much reduced in size as 

 the splint bones in Equus. Their proximal ends and the 

 greater part of their shafts are placed well behind metacarpal 



